This image highlights the fibers in an owl monkey’s hippocampus, a brain structure that lies at the heart of our ability to learn and remember. The red and white fibers are entering the hippocampus. “There is clearly extraordinary three-dimensional structure to the connections of the hippocampus, which is presumably important in coding information,” says Wedeen. “Only in a few instances do we know what the organization of these fiber bundles is.”

Understanding the structure of these subunits of the brain could shed light on how they work, as well as on how they develop. “We believe curvature of fibers may encode the otherwise unobservable developmental sequence,” says Wedeen.